When we write a formula of a compound in its simplest form, it is empirical formula.
Given the molecular formula is = C₁₈H₃₆
Now we can relate both empirical and molecular formula as;
Molecular formula = n x empirical formula
C₁₈H₃₆ = 18 x CH₂
So the empirical formula of C₁₈H₃₆ is CH₂
To find pH, use the following formula ---> pH= - log [H+]
so first we need to calculate the [H+] concentration using the OH concentration. to do this, we need to use this formula--> 1.0x10-14= [H+] X [OH-], so we solve for H+ and plug in
[H+]= 1.0X10-14/[OH-]---> 1.0 x 10-14/ 1.0 x 10-4= 1.0 x 10-10
now that we have the H+ concentration, we can solve of pH
pH= -log (1.0x10-10)= 10
answer is A
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= 0.001 
. Therefore 200 
. Hope this helps.